Abrasive cleaning devices commonly referred to as sandblasters, have been used for a considerable number of years in the cleaning industry for cleaning various surfaces. Heretofore, a supply of abrasive particles, such as sand, is entrained in a stream of high pressure air and fed into a nozzle from which it is ejected and impinged against the surface to be cleaned. The high pressure abrasive particles remove dirt and debris from the surface and provide an extremely satisfactory cleaning means. However, considerable problems are involved with such abrasive cleaning operations. Many of the cleaning operations are performed in enclosed places such as the interior of tank cars, ships' hauls, or in factories and other locations where the spent abrasive particles and debris enter the air and become deposited on the surrounding equipment. Also, when the cleaning is done in a confined place, the duct that is created is so intense that the blasting can be performed only for short periods of time after which the operator must wait until the dust settles and visibility increases before continuing. This results in wasted time and increases considerably the cost of the cleaning operation. The generated dust also is a serious problem even when the cleaning operation is performed in outside environments due to the pollution created thereby.
Devices have overcome this problem by removing the spent abrasive particles and debris from within the cleaning nozzle by placing a vacuum thereon. In these devices, the spent abrasive particles and removed debris is retained within the nozzle housing and is withdrawn from the housing by a vacuum and returned to a collection on recycling equipment. This enables the spent abrasive particles to be reused thereby increasing the cost efficiency of the operation and prevents the removed paint, rust, and other debris from the cleaned surface from being ejected into the surrounding atmosphere. Examples of such pressurized abrasive systems having the vacuum recovery system are shown in U.S. Pat. Nos. 2,723,498; 2,846,822; 4,045,915; 4,433,277; 4,395,850; and United Kingdom Pat. No. 764,174.
Although these prior devices do perform satisfactory for many cleaning operations, they do have the disadvantage of not permitting the operator to view the surface while it is being cleaned. Although this is not a problem for many cleaning operations, it does present a problem for the abrasive cleaning of thin skinned or sensitive material such as used in aircraft, certain molds, fiberglass, or similar materials and structures. If the dwell time, that is the length of time that the pressurized abrasive stream is directed against one particular area, is excessive for such thin skinned material, the material will be distorted and damaged.
This problem has required many thin skinned and sensitive type materials to be cleaned by other methods such as chemicals. For example, in the aircraft industry, nearly all planes cannot be cleaned abrasively due to the sensitivity of the skin or thin metal of the aircraft and must be removed chemically. This cleaning operation requires a considerable amount of time and expense and in addition, creates a toxic, hazardous material or byproduct that must be disposed of properly.
Recently plastic abrasive particles have been developed which have found considerable success in the cleaning of such thin skinned and sensitive material. The lightweight of the plastic abrasive enables a low pressure to be used for impinging the plastic particles against the surface being cleaned. The lower pressure is possible since the weight of the plastic is approximately one-third of that of the heretofore commonly used sand particles. Although these plastic abrasive particles have found considerable success in the cleaning of thin skinned materials, the cleaning devices used therefore still have the problem of not enabling the operator to accurately regulate the dwell time that the abrasive particle stream impinges against the surface since the operator cannot see the particular area being cleaned since it is hidden within the housing that forms the vacuum chamber. It is desirable that the operator permits the abrasive streams to impinge against the surface only long enough to remove the debris and paint. The ability to accurately control the dwell time reduces considerably the amount of time required for cleaning a particular surface as well as preventing possible injury to the surface by an excess dwell time.
Therefore, the need has existed for an improved abrasive cleaning device for use with plastic abrasive particles which enables the operator to see the stream of abrasive particles as it impinges against a surface thereby enabling the dwell time to be accurately controlled which heretofore was not readily possible with prior abrasive cleaning devices.
Another problem with prior abrasive cleaning devices is that the cleaning head or vacuum chamber forming housing required two hoses to be connected to the housing. One hose, commonly referred to as the blast hose, carries the pressurized stream of abrasive particles, and the other hose, referred to as the vacuum hose, is attached to the cleaning head and source of suction to create the vacuum within the housing to remove the spent abrasive particles and debris. These two hoses increase the difficulty for the operator to manipulate the cleaning head in contrast to a cleaning head or device requiring only a single hose.
U.S. Pat. No. 4,212,138 which is believed to be the closest disclosure of the subject invention, discloses a sandblast cleaner in which a flexible hood or shroud is mounted on the end of a usual blast nozzle for confining the spent particles with the shroud. The shroud is provided with a small transparent window formed of a clear plastic material which is sewn into the shroud. The shroud is formed of a flexible woven fabric material which is pervious to air. Although such a device is satisfactory for small certain operations, it would be ineffective for large cleaning jobs, such as an aircraft, since the shroud would have to be continuously emptied manually of the spent abrasive particles and debris. Also the plastic window cannot be located close to the abrasive particle stream and work surface since the particles would hit and scratch the inside surface of the plastic window within a relatively short period of time making its usefulness seriously limited.